Adaptive Hypertext Transfer Protocol (HTTP) streaming is becoming a dominant content streaming technique, where HTTP live streaming (HLS), Smooth streaming (IMS) and 3GP Moving Picture Experts Group Dynamic Adaptive Streaming over HTTP (MPEG-DASH HTTP) are but some examples of existing techniques adapted for such distribution of content.
Those adaptive HTTP streaming techniques all have a common principle, namely that a client receives a content stream as a sequence of files, or media segments, as a sequence of byte-range requests, which are then decoded and played out as a continuous media stream Uniform Resource Locators (URLs) of a file sequence are described in a manifest file which is referred to as a .m3u8 playlist when used for HLS, an .ismc when used for ISM and a Media Presentation Description (MPD) when used for DASH.
A client of a user equipment (UE) may, after having acquired a manifest file, acquire one file after the other, as described in the manifest file. During file download, the client estimates the available link bit rate or the download speed, and depending on the difference between the available link bit rate and the encoded bit rate of the acquired media, the client can select an appropriate representation, which is typically slightly lower than the measured bit rate.
To prepare a continuous media stream of content which is suitable for HTTP streaming, the media stream is segmented into files, or media segments, on the server side, from which the media content is distributed, while, on the client side, these media segments are fetched one-by-one as independent files. The client may then play the files contiguously, thereby providing a continuous stream playout.
Multimedia Broadcast Multicast Services (MBMS) is a point-to-multipoint interface specification for existing and upcoming 3GPP cellular networks which is designed to provide efficient delivery of broadcast and multicast services, both within a cell as well as within the core network, such as e.g. Wideband Code Division Multiplex (W-CDMA), Enhanced Data Rates for Global System Global System for Mobile Communication (GSM) Evolution (EDGE), General Packet Radio Service (GPRS), Code Division Multiple Access 2000 (CDMA2000). Evolved Multimedia Broadcast Multicast Services (eMBMS) is a corresponding specification adapted for Evolved Packet Systems, including (Evolved Universal Terrestrial Radio Access Network) (E-UTRAN) or Long Term Evolution-System Architecture Evolution (LTE-SAE).
One typical use case for use of any of these specifications may be to deliver sport game video content to a large number of mobile phone users which are gathered in a sports stadium or any other location which is attracting a lot of people at the same time. MBMS or eMBMS can use the User Datagram Protocol/protocol via File delivery over Unidirectional Transport (UDP/FLUTE), as specified in RFC 3926, HLS or DASH as a Download Delivery Method to deliver live TV content to the mobile phones. Also popular files, such as e.g. Android updates, YouTube clip pre-loadings, or major news events may efficiently be distributed to a large number of recipients in this way.
According to the DASH specification, 3GPP TS 26.246 a 3GP/MPEG DASH encoder can generate audio and video tracks for one single streaming session in different files, as indicated in FIG. 1, where a first audio file 121 is separated from a first video file 122, and a second audio file 131 is separated from a second video file 132.
FIG. 2 is a simplified illustration of a MBMS system 200, where a Broadcast Multicast Service Center (BM-SC) 201 is distributing media content to User Equipments (UEs) 202, such as e.g. mobile devices or any other type of MBMS enabled User Equipment, via a Gateway (GW) 203 and an eNB 204.
In case DASH files are sent via an MBMS delivery system, the BM-SC will continuously transmit DASH files provided from the GW through a FLUTE session and typically a Forward Error Correction (FEC) redundancy level will apply on each file in order to increase the reliability of the FLUTE session.
There are, however, several drawbacks with sending DASH files with separate audio and video tracks in separate files over MBMS file delivery, especially since the audio file size is commonly relatively small, which results in that the BM-SC will need to apply separate FEC encoding on the audio files and the video files. Audio files are commonly more prone to losses than video files due to its relatively small size. A 2 second long audio file with 32 kbps will e.g. result in a 8 kbyte audio file. If the BM-SC applies a 10% FEC redundancy level and the encoding symbol size is 1024 bytes, 11 encoding symbols will be delivered by the BM-SC in the session. In case any two encoding symbols are dropped during distribution, the UE will not be able to recover the audio file.
In addition, from a UE point of view the excessive FEC decoding which is required for capturing all files will have a negative impact on the battery consumption.
Therefore, there is a desire to find a more efficient way of distributing media content comprising both audio and video files.